fear_greed_index

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It effectively describes the tool's behavior: returning a value with classification and optional history, and discloses the cost per call ($0.001 USDC). However, it doesn't mention rate limits, authentication requirements, or error conditions.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is efficiently structured: first sentence explains the core functionality, second provides usage guidelines, third details return values, and fourth discloses pricing. Each sentence adds essential information with zero wasted words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a single-parameter tool with no annotations and no output schema, the description provides good context: purpose, usage, return format, and pricing. It could be more complete by describing the history array structure or error cases, but covers the essentials well given the tool's moderate complexity.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema has 100% description coverage, so the baseline is 3. The description adds value by explaining that the parameter controls 'optional history' and that the tool returns 'value (0–100), value_classification, optional history[]', providing context beyond the schema's technical specification of 'limit'.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: to retrieve the Crypto Fear & Greed Index with optional historical data. It specifies the scale (0-100) and classifications, distinguishing it from sibling tools like token_price or crypto_news that serve different market analysis functions.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly states when to use this tool: 'when you need to gauge overall crypto market sentiment or mood — whether the market is fearful or greedy.' This provides clear context for selection versus alternatives like token_price (specific pricing) or crypto_news (news-based sentiment).

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.